Short nanotubes carry big currents

December 1/8, 2004

Researchers from Stanford University have
developed a simple way to fabricate carbon nanotube devices whose length
is as small as ten nanometers, and have shown that electricity can pass
through the nanotubes very efficiently.

Ordinarily electrons traveling through wires and devices bounce
off the atoms of materials. In small enough devices, however, electrons
can travel ballistically, or straight through, which greatly increases
efficiency. Carbon nanotubes are rolled-up sheets of carbon atoms that
can be narrower than a single nanometer. A nanometer is one millionth
of a millimeter, or the span of 10 hydrogen atoms.

Short carbon nanotubes could eventually be used as ballistic transistor
channels and interconnects in tiny circuits, according to the researchers.

The researchers found that 10-nanometer-long, two-nanometer wide
carbon nanotubes with metallic properties were capable of carrying four
times more current -- about 100 microamps -- than longer nanotubes, and
4,000 times more current by size than copper wire at room temperature.
They also found that 50-nanometer-long carbon nanotubes with semiconducting
properties were capable of fast, low-power operation -- about 25 microamps
at a fraction of a volt.

The researchers grew arrays of carbon nanotubes, used standard
chipmaking techniques to place metal electrodes at one end of the array,
then deposited metal atoms at an angle to the surface. The electrodes
blocked the atoms from covering a narrow area, leaving short lengths of
the nanotubes intact between pairs of electrodes.

Existing nanotube fabrication methods tend to use electron beam
lithography, which is useful for making a few devices, but is not practical
for making the numbers of devices need for commercialization.

The method could be used practically in five to ten years. The
work appeared in the September 14, 2004 issue of the Proceedings of
the National Academy of Sciences.